Engine/Transmission (1998.5 - 2002) Another Oil Question

[Good Ole Bob]

Today when I filled up my fuel tank, I checked my oil level, and found it almost a quart low! The engine only has 36,0768 miles on it, and it has never been low before. On my last oil and filter change, 8,421 miles ago, I changed from Rotella 15w40 to the senthic Rotella T 5w40. Could this be the problem? I usually change the oil and filter fairly often. With only 36,078 miles, I have change the oil 6 times, and that is 6,013 miles each time. The truck is driven only on the highway, and ocasionly pulls a trailer and tractor. Has any one else tried this oil. I get my oil from Wal Mart, and the filter from Dodge. Can I go back to regular oil, or do I have to stay with the new stuff?

 

[B.G. Smith]

Oil

I am no authority on oil but I would say the 5w40 is too light for around here. I have used Rotella14w40 since my truck was new and now have 86,000 miles and it has never been low at change, I change at about 3500 miles though, pull a 5th wheel some. bg

 

[Good Ole Bob]

Thanks for the responce. Now, can I go back to the old fossil oil without hurting anything. I'm like you, I think that this oil is too thin for this area.

 

[DocStressor]

I wouldn't give up on the synthetic just yet. But I would change out the oil pretty soon. It's not unusual to see an increase in oil consumption immediately following a switch to synthetic. The synthetic oil disperses the oxidized material that coats the engine parts as the result of running conventional oil for a while. The result can be a rapid deletion of the additive package, which could lead to increased oil consumption. That’s why most companies recommend against going to an extended drain interval until your second change after a switch to synthetic.



Change the oil and filter and check if you still see increased oil consumption with the next batch. If you still have a problem, you can always go back to conventional oil at any time. BTW, you can run 5W-40 in any climate. The viscosity at operating temperature is essentially the same as 15W-40. That's why I doubt that viscosity is the cause of your increased consumption.

 

[Good Ole Bob]

Lee, thanks. . I think that I'll change the oil and filter tomorrow. Then I'll keep a close eye on it, and see what happens. I have heard that you should not change back to regular oil, after using synthetic ; but, I just talked to a former mechanic, and he said that it would not hurt anything at this point. I did not think that it would, but I wasn't sure. Bob

 

[dalton4]

Remember there is a quart or two of oil our in the engine that has to drain back into the pan. If I check my oil right after shut down it will show 1 - 1 1/2 qts low. The level will be back up to full after the oil drains back into the pan.



You stated that you checked the oil when you were fueling the truck. This doesn't allow much time for drain back and may be the reason for the lower oil level.



Jerry

 

[dalton4]

BMatlock, reading from the "view new posts" section I failed to notice that you are packing 12 extra valves. Not having the P-7100 you wouldn't likely have as much oil drain back to pan as I do.



Jerry

 

[amsoilman]

If you are running a synthetic oil, always wait for at least 5-6 hours after engine has been shut down before checking the oil or it will read low on the stick. I have seen this phenomenon happen with the Amsoil synthetics. It takes much longer for the oil to drop off the upper end of the engine parts before it gets back to the pan. Incidentally, a synthetic 5W-40 oil and a 15W-40 petroleum oil are the same Viscosity at the operating temperatures as Lee Webber stated.



Wayne

amsoilman

 

[John Berger]

Are you sure your using/losing oil?

Here's why I ask that. I'll keep this as short as possible. From the time I bought my truck until early this summer, my dipstick level always measured what I would deem a quart above the full mark. Came from the factory that way. Every oil change I did after that, I would allow to drain thoroughly, put one quart in the filter and 10 in the crankcase. Same level on the dipstick. Forward to this summer. I'm towing my soon to be deceased travel trailer home from Wisconsin. I stop for fuel at a truck stop, proceed to fill up and when I'm done I check the oil. It looks like it's about a quart low. I add a quart and move on down the road. This was in early June. I decide to start checking the oil a bit more than regularly and I notice that it now only occasionally even registers above the full mark. I posted a couple of threads on this matter, wondering if I was developing a problem. I run Amsoil 15W-40 in the motor and change the oil between 9-10K miles, with a filter change every 5K. Oil analysis comes back A-OK, my wear metals are below universal averages. I can't find the first damn leak. The turbo is clean and dry, same as the tailpipe (minus the soot of course) So, I'm wondering what the heck is going on. For over 72K miles, the dipstick level was consistent, now it's all over the map. I did a complete oil change a couple of weeks ago and guess what? With 11 quarts of oil, my dipstick hardly reaches the full mark, the first time I run it and then check for leaks and the level. This was 15 minutes after I put the new oil in. I have absolutely no idea why. Sometimes it's over the full mark, sometimes, it's at the mark. You may really not have a problem. Sorry for being so long. I hope this helps your piece of mind.

 

[B.G. Smith]

5W

Some years ago when auto makers first started promoting 5w30 oil for autos there was an article written by an engineer who stated that the main reason for the 5w was fuel economy and that some engine wear however small could be expected with its use over the 10w oils. I realize that in colder climates the lower viscosity oils are a must and promote longer engine life. Living in a climate where the average temperature year round is probably near 80 degrees, I have opted to stick with 10w30 oil in my gasoline vehicles and have run straight 30 weight during the summer month a few years ago. Being one who keeps a vehicle longer than most I have had the opportunity to see some internal engine parts after well over 100,000 miles and was pleased with the wear or lack therof. As for me and my house, I'll stay with the 15w40 in my Cummins and 10w30 in my gas jobbers. bg.

 

[fest3er]

Originally posted by amsoilman
... Incidentally, a synthetic 5W-40 oil and a 15W-40 petroleum oil are the same Viscosity at the operating temperatures as Lee Webber stated... .

Wayne and Lee,

This question came up recently. I reasoned. as do you, that at operating temperatures, 5W40 and 15W40 have the same viscosity.

My concern was that, when the engine is cold (in, say, 40F ambient temp), the 5W40 oil might be too thin to provide adequate lubrication. However, when the ambient temp is -20F, the 5W40 should provide *better* lubrication when the engine is cold. I suggested that 5W40 would be great in winter, when the temps run from -20F to +50F, but that 15W40 would be better in the summer, when temps are generally 50F-110F.

But I still have a niggling doubt. So I will ask a few technical questions.

Consider 5W40 and 15W40 oils across the temperature range from, say, -40F to 300F.

• Is the viscosity linear across this range?
• Or is it reasonably linear? or completely non-linear (that is, stays at the 'W' weight for a long time, then jumps rapidly to 40)?
• Are 5W40 and 15W40 vastly different in this respect (other than the difference between the 5W and 15W)?
• Are graphs available that show the typical viscosity of multi-weight oils across the temperature range?
• Do synthetic oils 'perform' differently, in this respect, from non-synthetic oils?

Well presented, this info could help all of us better understand how temperature affects the dynamics of engine lubrication.

Thanks,
Fest3er

 

[amsoilman]

Fester,

First off, one must uderstand the term "viscosity. " When a fluid is subjected to external forces, it resists flow due to internal molecular friction. Viscosity is a measure of that internal friction.

So, Viscosity becomes the most important characteristic of a lubricant.

Viscosity can be viewed in two different ways. The first is a fluid's tendancy to flow as is visually indicated. One can think of this as the time it takes to watch a fluid pour out of a container. The term used to describe this is Kinematic Viscosity and it is expressed in units indicating flow volume over a period of time.



The most commonly used unit of Kinematic Viscosity is the Centistoke (cSt) . Another is a Saybolt Universal Second (SUS or SSU).



When comparing the Viscosity of two different fluid's, keep in mind that a Centistoke and a Sabolt Universal Second are two different Units. Therefore, they cannot be accurately compared.



The temperature of the fluid being tested will also affect the outcome. The Kinematic Viscosity of a fluid is determined at 100 C (210 F) and or 40 C (100 F) depending on the grading system being used. For general comparison purposes, the temperature at which the Viscosity was determined has to be the same.



The second way Viscosity can be indicated is through measured resistance. You can think of this as the energy required to move an object through the fluid. It takes little energy to stir water with a spoon. However, significantly more energy is required to stir honey with that same spoon. The term used to describe this is Apparant Viscostiy and it is expressed in units known as Centipoise (cP).



The SAE has established 12 Viscosity grades that are suitable for engine lubricating oils. This is known as SAE J-300 Engine oil Classification, Dec 1999 The high temperature Viscosity for all engine oils is always determined at 100 C. Muli-grade oils must meet the requirements for both high and low temperatures.

Are graphs available that show the typical viscosity of multi-weight oils across the temperature range?

Yes ther are graphs that will show this. I will try to explain the differences without doing a graph.



An SAE 10W will be suitable for low temperature application, but will thin readily as the temperature increases. The "single" grade oil such as a SAE 30 is suitable for high temperature applicaitons, but will thicken readily as the temperature decreases.



The multi-grade oil such as a 10W-30 maintains its Viscosity throughout, which makes it suitable for use over a significantly broader temeprature range.



There are certain "Base Stocks" that may have the ability to function over broader temperature ranges, but most Mult-grade oils start with a "Base Stock" possessing the desired Low temperature Properties, and add Viscosity Index Improvers to reduce thinning as the temperature rises. We're talking oil temperatures here.



There are a number of other things that effect the Viscosity over a given temperature range as well. One of them is Viscosity Index. (VI) Viscosity Index is an empirical number indicating the Degree of change in Viscosity of an oil within a given temperature range. A low VI number indicates a relatively large change. Numbers of 60 or below are considered low. A high VI number will indicate the ability to provide protection over a wider temperature range.



Hope this helps,





Wayne

amsoilman

 

[HC]

Edit, new answer:



You said 8421 since last change, and 36078 total. That means for your first five oil changes, you averaged only 5531 miles per change. This time, you went 52% further. If you drove only 4,000 to 4,500 on some of those changes, then you may have driven twice as many miles this time around as on some of your earlier runs. Since you drove a lot further, it would be normal to use a little more oil, where maybe you hadn't noticed any drop before.



Even if you really did use a quart in 8421 miles, that is not something to be concerned about, IMO. That's still a good, tight engine. Since you changed weights, a slight change in consumption might be expected. The only comments I could add to what has already been said is take a look at your breather bottle, you might have a little more there than before.



If you want to go a little longer on synthetics, I would recommend you go to about a 10k change interval, but change the filter at 5k and top up with oil at the filter change. Once a filter begins to get dirty it just bypasses oil to protect the engine, but you have no way to know that is happening. I don't like going longer than 5k per filter change for that reason. Also, I wouldn't go longer than 10k without a bypass filter system, even though a number on this board feel comfortable doing that.

 

[fest3er]

Originally posted by amsoilman
... The multi-grade oil such as a 10W-30 maintains its Viscosity throughout, which makes it suitable for use over a significantly broader temeprature range.

There are certain "Base Stocks" that may have the ability to function over broader temperature ranges, but most Mult-grade oils start with a "Base Stock" possessing the desired Low temperature Properties, and add Viscosity Index Improvers to reduce thinning as the temperature rises. We're talking oil temperatures here. . . .

Thanks, Wayne. I think it does make the concept somewhat clearer. But let's see if I can properly summarize.

Going back to my previous question (which had to do with the difference between a 5W40 and a 15W40 oil), would it be fair to say that the viscosity of each oil meets the ... 'lubricating properties' required by the Cummins 6B across their respective temperature ranges? Worded differently, will both of the oils maintain the same load-bearing oil fillm (such as that found in the con-rod to crank bearing) across their temp ranges?

So the only real difference between the two grades, then, is the 5W40 maintains that required viscosity tdown o -10F, whereas 15W40 only maintains the viscosity down to 10F?

And to return to my *other* question, does this then mean that 5W40 can safely be used in an engine year round, with ambient temps ranging from -10F to 110F, since it has the required viscosity across the range?

And a new question: why, then, would Dodge suggest using 10W30 (or synth 5W30) in the Cummins when the ambient temp is between -10F and 30F? Doesn't it have a lower viscosity in general? Or did they take into consideration the fact that the engine will produce less power in frigid temps (due to winter blend fuel and other factors)? And less power means less load on the oil films...

Yeah, I'm just *full* of questions today!

Thanks,
Fest3er

 

[DocStressor]

fest3er- I e-mailed you about more specific answers to you question. The general answers are as follows:



1. Is the viscosity linear across this range?



Yes, but the slope of the line relating temperature and viscosity is much smaller (or flatter) for synthetic oils having higher viscosity indexes.



2. Or is it reasonably linear? or completely non-linear (that is, stays at the 'W' weight for a long time, then jumps rapidly to 40)?



Viscosity is a function of the amount of energy holding the molecules of a fluid together. As heat energy is added to a system, molecular motion increases and the amount of cohesive energy between the molecules decreases. Thus, viscosity of a solution decreases linearly with temperature up to the point where chemical changes in the molecules occur. The upper limit is usually near the flash point of the lubricant.



3. Are 5W40 and 15W40 vastly different in this respect (other than the difference between the 5W and 15W)?



According to the SAE viscosity grades for engine lubricants table, the "W" number is determined by the absolute viscosity of the oil at a given temperature. The units are in centipoise (poise = the amount of force in dynes required to move a surface 1 square cm in area past a parallel surface separated by a 1 cm thick fluid film at a speed of 1 cm per second). A 5W oil has an absolute viscosity limit of 3500 cP at -25 degrees C. A 15W oil has an absolute viscosity limit of 3500 cP at -15 degrees C. The "upper" viscosity range of 40 is expressed as kinematic viscosity (absolute viscosity divided by density) at 100 degrees C (212 F). The range for 40 weight oil is between 12. 5 to 16. 3 cST. So as you increase the temperature of a 5W-40 oil from say -25 degrees C to 100 degrees, the viscosity decreases at a slower rate that for a 15W-40 oil that starts out at a higher viscosity at the lower temperature.



BTW, these are the numbers from the old SAE tables. They have recently been revised, so 5W and 15W aren't quite what they used to be.



4. Are graphs available that show the typical viscosity of multi-weight oils across the temperature range?



Yes, I believe that the SAE has graphs available for 6 standard oil viscosities.



5. Do synthetic oils 'perform' differently, in this respect, from non-synthetic oils?



Yes, the higher VI of synthetics (including Group III oils like Rotella synthetic) have flatter temp/viscosity curves than conventional oils without the addition of viscosity improvers. For example, a 40 or 50 weight polyol ester based oil already meets the 15W absolute viscosity rating without viscosity additives. This has a large effect on how the oil performs in the engine vs the lab bench. Motor oils are "non-Newtonian" fluids. That means that the viscosity will be reduced by shear stress as the oil flows in a narrow film as well as by temperature. Oils with viscosity enhancers added generally shear to lower viscosities in bearings, rings, and cam followers than oils that don't need these additives. The other advantages of synthetics have been discussed in many of the oil threads on this board, so I won't mention them here.



In summary, an ideal oil for the Cummings would maintain a kinematic viscosity of 12. 5 cSt at all temperatures between -35 and 300 degrees C. However, no such fluid exists within the boundaries of chemistry and physics. So the next best thing is an oil with as high a VI as possible. A 5W-40 oil is never too thin to provide protection at intermediate temperatures. The only way at 15W-40 oil might provide increased protection at high temperature vs a 5W-40 oil (assuming equal additive packages, etc. ) would be if it was formulated toward the high end of the 40 weight range (16. 3 cSt). But the difference in protection would be minor and the higher viscosity would extract a fuel milage penalty.

 

[amsoilman]

Fester3,

Going back to my previous question (which had to do with the difference between a 5W40 and a 15W40 oil), would it be fair to say that the viscosity of each oil meets the ... 'lubricating properties' required by the Cummins 6B across their respective temperature ranges? Worded differently, will both of the oils maintain the same load-bearing oil fillm (such as that found in the con-rod to crank bearing) across their temp ranges?

Yes, the load bearing properties of both the 5W-40 and the 15W-40 oils would be the same at the "operating" temperature.

And a new question: why, then, would Dodge suggest using 10W30 (or synth 5W30) in the Cummins when the ambient temp is between -10F and 30F? Doesn't it have a lower viscosity in general? Or did they take into consideration the fact that the engine will produce less power in frigid temps (due to winter blend fuel and other factors)? And less power means less load on the oil films...

I think Dodge may figure the 10W-30 and 5W-30 synthetics may flow better in the colder temps... ... That is my opinion only. I realy do not know why they would suggest that.



Personally, I use the 5W-30 Amsoil year around.



Wayne

amsoilman

 

[DocStressor]

More Questions

Neal, you are indeed full of questions. Ok, now I think I understand what is confusing you. We have to distinguish between "lubricating" and "load bearing" properties of an oil. The load bearing properties are directly related to the viscosity of the lubricant under high temperature/high shear conditions. Both temperature and shear decrease viscosity and thus the load bearing ability of an oil film. The relationship between temperature and viscosity is straight forward as explained above. The load bearing capacity decreases with the square root of viscosity. That means that a 50 weight oil with a kinematic viscosity of 18. 6 does not have twice the load bearing capacity of a 30 weight oil with a kinematic viscosity of 9. 3 cSt. Also, the actual viscosity of an oil film in a bearing journal, for example, is not simply a function of the temperature of oil coming from the sump, since shear forces are a major factor as well. Oils with synthetic base stocks have significantly higher load bearing capacities that conventional oils at any given viscosity level since they are intrinsically more shear resistant. They also tend to run cooler because of lower frictional coefficients, which tends to maintain viscosity. All of this has to do with the size and shape of the lubricants at the molecular level.



Comparing apples to apples, a 40 weight oil conventional oil will have a higher load bearing capacity than a 30 weight. Similarly, a synthetic 40 weight will have a greater load bearing film strength than a 30 weight synthetic.



Now before everyone goes out a buys 90 weight oil, we have to consider engine design. All Cummins engines have very large bearing surfaces relative to their displacement. That mean that the load on a bearing is spread out over a larger surface area so the load on the oil film at any giving pont is not that high. The oil in the bearing gets replaced with cooler oil pumped up from the sump at a good rate. The rate of that flow is inversely proportional to viscosity, so oil that is too thick at operating temperatures doesn't flow into the bearings (or rings or anything else) at the proper rate. The result can be increased heating of the oil in the bearing leading to a local decrease in viscosity that can result in increased wear. So the point is that every engine is designed to operate with oil within a certain viscosity range. For our engine it is 40 weight. Too low a viscosity leads to oil film break down under load and increased wear. Too high a viscosity can lead to exactly the same thing because of poor flow characteristics. So when you rev up a cold engine under load before the oil warms up, you can have oil film break down at critical engine surfaces, just as if you were running 90 weight oil. So there is a real lubrication advantage of a 5W oil over a 15W oil upon startup and until the engine reaches operating temperature. Of course the lower the ambient temperature, the greater the advantage.



Why does Cummins recommend 5W- or 10W-30 oils at extremely low temperatures? For the reasons explained above. They don't recommend 5W-40 oils because they have not been generally available. You can't make a conventional oil that spans the 5W-40 viscosity range because of the VI limitations of conventional base stocks. The only 5W-40 that has been around until recently was Delvac. Now with the advent of cheaper Group III base stocks, we are seeing lots of 5W-40 oils showing up in the market place. They have the advantage of the cold flow characteristics of a 5W-30 oil and the high temperature protection of a 40 weight. I is just a matter of time until all diesel engine manufacturers start recommending 5W-40. Of course some, like Ford, will recommend lower viscosity oils. But that has more to do with fleet fuel economy averages than engine durability. The lower the viscosity, the lower the drag, the better the mileage.

 

[Riflesmith]

Lee,

Excellent, informative post. It explained everything very well.

 

[Cooker]

Great thread. I would like to thank those who have contributed.



Take care,

Ryan

 

[Cliffman]

Awesome post Lee. Man I'm glad there's guys like you still posting on this board. I live in San Jose, Ca. I've been using Amsoil 5-30 in my truck for 80K miles now. After reading all these oil threads I'm still not sure if I should be running 5-30 or 15-40. Based on horsepower (410) and geographic location, I'm considering keeping with the 5-30 during winter months and changing to 15-40 during summer months. All Amsoil of course. What do you think? Also, I change filters every 3k and after 9k I change the oil.